In conventional cars, a windowpane is moved up and down by manually rotating a handle. In more automated cars, however, an arrangement called "power window device" is employed to automatically move a windowpane up and down.
One arrangement of these automatic windowpane devices includes a drive motor rotatable in two opposite directions, a switch for changing the motor rotation for upward or downward movement of a windowpane, and two pairs of monostable multivibrator circuits. The multivibrator circuits produce a trigger pulse to drive the motor for a time to effect upward or downward movement of the windowpane.
The time for activating the motor is fixed in the aforegoing windowpane device regardless of where the windowpane is positioned before it is driven. Therefore, if the windowpane is moved up or down from a half-opened position, the motor continues its rotation also after the windowpane has reached its upper or lower limit. This apparently increases the load to the motor. If this use is often repeated, the life of the motor is significantly reduced.
Also when a solid foreign matter or obstacle such as human neck or arm is inadvertently sandwiched between the upper margin of the windowpane and the upper window frame during upward movement of the windowpane, the upper margin of the windowpane continuously applies a compressive force to the neck or arm until the fixed time of the motor rotation expires. This is a great danger for a family including little children.
There are many proposals for overcoming this problem by using a detection means for detecting that any solid matter is sandwiched between the upper margin of the windowpane and the upper window frame during upward movement of the windowpane.
In a prior art automatic windowpane device, a motor receives an electric current having a waveform shown in FIG. 4 while it drives a windowpane. The waveform defines the current on activation of the motor at (a), during normal movement of the windowpane at (b), and on a blockage of the windowpane by a solid body at (c).
FIG. 4 shows that the current (c) on a blockage suddenly becomes much higher than the current (b) during normal movement of the windowpane. This phenomenon is used in the prior art arrangement so that a motor is deenergized when a blockage detector detects a current value exceeding a reference level, and judges that the windowpane has been blocked halfway by a solid matter in the moving path thereof. This arrangement, however, requires a means for discriminating the motor starting current (a) from the abnormal current (c) due to a blockage because the detector will otherwise erroneously acknowledge that current (a) representing a similarly great increase must be the abnormal current (c) caused by a blockage.
Instead of measuring the motor current, another prior art arrangement is adapted to monitor the motor revolution to deenergize the motor on detection of a significant decrease in the revolution due to a blockage of the windowpane.
The both aforegoing prior art arrangements are adapted to measure the absolute value of the detected material so as to acknowledge a blockage if the absolute value is out of a reference level, and stop the motor. However, the current and revolution of the motor are readily affected by various materials such as deformation of a window frame, ambient temperature, discharge voltage drop of a car battery, etc. Therefore, the reference level for judgement of existence or absence of a blockage must be considerably high in the motor current detecting arrangement and considerably low in the motor revolution detecting arrangement. These requirements prevent a sufficiently effective operation of the automatic windowpane elevator.
The present applicant already proposed a windowpane automatic elevator disclosed in a Japanese patent application No. 157298/1984 and filed July 30, 1984 which is directed to resolution of the aforegoing problems. The prior application provides an arrangement comprising a drive motor for moving a windowpane up and down, and a detector means for detecting that part of a human body or other solid matter is sandwiched between the upper margin of a windowpane and an opposed window frame during upward movement of the windowpane. The arrangement further comprises a sensor means for sequentially measuring a motor characteristic such as voltage, current, revolution, or other material of the motor; and a comparator means for comparing present and preceding values detected by the sensor means and producing a blockage detection signal when the deviation obtained by the comparison exceeds a predetermined level.
It should be noted, however, that car window frames are often deformed for some reasons, and windowpanes are not readily received in proper positions with respect to the window frames. In this case, a blockage will occur before the windowpane reaches its upper limit. This will be erroneously deemed to be a blockage by a foreign matter, and the detecting function wil be effected to invert the movement of the windowpane from upward to downward direction. This problem is not overcome by the prior application.